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Posted: Wed Nov 14, 2018 11:34 am
Is the VSEPR group the names of the shapes of the Lewis structure? I'm so confused.
Posted: Wed Nov 14, 2018 11:42 am
The VSEPR (valence shell electron pair repulsion) model helps predict the geometry of a molecule based on the the molecule's Lewis structure and its regions of high electron density. Since these regions repel one another, the shape of the molecule is affected. This is why the geometry changes when there are lone pairs on the central atom. Hope this helps!
Posted: Wed Nov 14, 2018 1:42 pm
Lewis structures are needed for the VSEPR model to determine the areas of electron density around the central atom (bond pairs and lone pairs). From this information obtained by drawing a Lewis structure, the molecular shape can be determined.
Posted: Wed Nov 14, 2018 1:48 pm
First, in order to find the VSEPR model for a molecule, you need to draw the Lewis structure. This is a 2D demonstration, and says nothing about the bond angles. To determine the shape, use 3 dimensions to find the angles that each atom (and therefore the electron densities) are as far apart as possible. For example, most 5-atom molecules are tetrahedral, with bond angles of 109.5 degrees, rather than 90 degrees, which one might falsely predict if you were looking just at the Lewis structure.